This invention relates to a two stage hydroprocessing process with interstage stripping. More particularly, the interstage stripping occurs at high pressure and temperature with recycle of high temperature gaseous effluent from the stripping stage.
A common method to remove contaminants such as nitrogen and sulfur from a hydrocarbon feedstock is to use a hydrotreating step to convert the nitrogen and sulfur contaminants to hydrogen sulfide and ammonia followed by stripping to separate the gaseous effluent from the liquids. The stripping is typically conducted at low temperature and pressure. The hydrotreating step is frequently followed by a further hydroprocessing step containing a catalyst which is sensitive to the presence of sulfur and nitrogen contaminants.
Stripping steps involve considerable investment and operating costs as stripping usually involves depressurization and cooling followed by pumping and heating to repressurize and reheat the feed to the next hydroprocessing step.
It would be desirable to have an interstage stripping process which minimizes the investment and operating costs associated with stripping.
This invention relates to an interstage stripping process which reduces the investment and operating costs associated with stripping. Accordingly there is provided a continuous process for interstage stripping between two hydroprocessing zones which comprises:
a. passing a hydrocarbon feedstock to a first hydroprocessing zone and hydroprocessing the feedstock under first hydroprocessing conditions to form a first hydroprocessed product, said first hydroprocessing zone having a first hydroprocessing temperature and pressure;
b. passing the first hydroprocessed product to a first stripping zone;
c. stripping the first hydroprocessed product to form a first gaseous and liquid effluent;
d. passing the liquid effluent from the first stripping zone to a second hydroprocessing zone and hydroprocessing the liquid effluent under second hydroprocessing conditions to form a second hydroprocessed product, said second hydroprocessing zone having a second hydroprocessing temperature and pressure;
e. passing the second hydroprocessed product to a second stripping zone;
f. stripping the second hydroprocessed product to form a second gaseous and liquid effluent; and
g. passing at least a portion of the second gaseous effluent to the first stripping zone and contacting said second gaseous effluent with the first liquid effluent.
Another embodiment relates to a continuous process for interstage stripping between two hydroprocessing zones which comprises:
a. passing a hydrocarbon feedstock to a first hydroprocessing zone and hydroprocessing the feedstock under first hydroprocessing conditions to form a first hydroprocessed product, said first hydroprocessing zone having a first hydroprocessing temperature and pressure;
b. passing the first hydroprocessed product to a first stripping zone, said first stripping zone including a flash separator and a pressure stripper;
c. flashing the first hydroprocessed product to form a first gaseous and liquid effluent;
d. passing the first liquid effluent from the flash separator to the pressure stripper and stripping the liquid effluent to form a second gaseous and liquid effluent;
e. passing the second liquid effluent from the first stripping zone to a second hydroprocessing zone and hydroprocessing the liquid effluent under second hydroprocessing conditions to form a second hydroprocessed product, said second hydroprocessing zone having a second hydroprocessing temperature and pressure;
f. passing the second hydroprocessed product to a second stripping zone;
g. stripping the second hydroprocessed product to form a third gaseous and liquid effluent; and
h. passing at least a portion of the third gaseous effluent to the first stripping zone and contacting said third gaseous effluent with the second liquid effluent.
The present process describes a method for removing nitrogen- and sulfur-containing contaminants from multi-zone hydroprocessing schemes without the need for disengagement, i.e., low-pressure stripping which involves depressurization, stripping and re-pressurization, and the attendant costs for such an operation.